We see it's a multiple of 2 and a multiple of 9 because the sum of the digits is 18.
Let's take out the factors of 2 and 3 and see what's left.
15552/2 = 7776
7776/2 = 3888
3888/2 = 1944
1944/2 = 972
972/2 = 486
486/2 = 243
243/3 = 81 = 3(3)(3)(3)
Putting it together,
